If a personal computer (PC) accesses a target site for destination via a communication network, there is a case that PC may be guided to a site (for example, a specific Web site or a fake site) other than the target site.
For example, spoofing in ARP (Address Resolution Protocol) is a fake IP (Internet Protocol) to use another person's IP address. In the spoofing, a router (fake router) guiding to a fake site fakes its IP address to IP address assigned to a true router (original router), via which a PC accesses the target site. Consequently, PC is guided to the fake site by the access's passing via the fake router. As a result, PC cannot access any site other than the fake site.
Encryption techniques are examples of measures against the above-mentioned “spoofing” or against stealing information transmitted and received via the communication network.
However, in the case of transmitting and receiving encrypted information, it is difficult for a gateway relaying the encrypted information to provide a highly value-added service. For example, PTL 1 (Patent Literature 1) discloses a relay device for providing the highly value-added service even in the case of transmitting and receiving encrypted information. The relay device uses an encryption technique called “Split SSL (Secure Socket Layer)”. The relay device decodes encrypted information transmitted based on Split SSL in the own device and provides a service by use of the decoded information.
Moreover, PTL 2 discloses an example of art using a spoofing. PTL 2 discloses a communication guiding device for reducing a load of a server in case of guiding communication. The communication guiding device guides communication by transmitting a fake ARP reply unless it has guided an IP address assigned to a source transmitting an ARP request. Then, the communication guiding device guides the communication by transmitting a DNS (domain name system) response representing an IP address of a server device for destination of the guidance in response to a DNS request guided by the fake ARP reply.